Space-based manipulators are known in the art. Advanced long-reach high-performance manipulators are needed to support in-space operations such as Near Earth Object berthing, telescope assembly and satellite servicing. Manipulators that can lift, translate and precisely position payloads, equipment and infrastructure on planetary surfaces are necessary to execute most space exploration missions. The requirements for these planetary surface devices include having long reach (to unload landers for example), package efficiently for launch, be able to exert large tip forces and have low mass.
It has been concluded that conventional (Earth-based) robotic manipulator configurations would have extreme difficulty meeting planetary surface requirements because their mass increases rapidly with increases in reach and payload handling mass. In Earth-bound applications, cranes are mass efficient devices that have long reach and high payload capability, but cranes lack the dexterity and versatility found in robotic manipulators.
In order to meet planetary surface requirements, a hybrid crane/manipulator, the Lightweight Surface Manipulation System (LSMS), was created. The LSMS is a cable-actuated manipulator that achieves high structural efficiency by using an architecture that reacts payload handling load through members acting in either pure tension or compression (as opposed to bending in conventional robotic manipulators). Further mass efficiency, achieved by using the tension structure (cables) to also articulate the LSMS arm hinges, is enabled by the mechanical advantage inherent in the tension/compression LSMS architecture. Lightweight hoists are used to reel cable in and out (thus articulating the hinge), replacing the massive high-torque motor gear-boxes used in a conventional boom manipulator.
In-space applications, just as in a ground-based application, for a desired applied tip force, the structural efficiency of a traditional boom/rotary-hinge manipulator architecture rapidly degrades as the manipulator reach is increased. The LSMS uses the tension/compression member architecture with tendon-controlled articulation architecture to achieve high structural efficiency. Similarly, a manipulator that is based on an architecture of tension-stayed booms and tendon-controlled articulating hinges has the potential to achieve the high structural efficiency necessary to make long-reach manipulators practical. The LSMS takes advantage of gravity and LSMS self-weight, plus the weight of the payload, to maintain tension forces in the cables during articulation. Cable stiffened structures have also been developed for many space applications and structures, but have never been considered as components in a space robotic manipulator.
There are many critical features that must be present in a manipulator if it is to be viable for space missions. The manipulator must be lightweight, stiff, package efficiently, reliably deploy and operate reliably. It is also desirable for the manipulator to have the ability to restow. For the case of a hyper dexterous manipulator (HDM), it must also have a large range of motion, allowing it to avoid obstacles away from the wrist/tip while reaching into difficult to access locations. A high level of dexterity can be achieved by using the traditional approach of using a large number of link-actuator pairs (with manipulator complexity increasing as the number of link/hinge pairs increases).
A major capability for a manipulator, defined as its stiffness, is the ability to apply a force at its tip/wrist without exceeding a specified level of deflection. High stiffness can be desirable to provide the tools/end effectors a stable platform off of which to work, to provide a high degree of stability and precision and/or prevent large deflections that might cause the arm to collide with surrounding objects. For a given tip force, as stiffness is increased, the deflection decreases. For a selected material construction, the stiffness of a tubular link, as found in most conventional manipulators, is increased by increasing the tube diameters. At some point, increasing tube diameter becomes impractical because of either packaging limitations, or the size of the tube impedes operations, or the ability to reach into tight spaces.
The articulating hinges in a manipulator are designed to apply a moment such that a force of a specified magnitude is generated at the manipulator tip/wrist. In a conventional manipulator, the hinges are typically actuated by motor-driven gearboxes that incorporate brakes on the motors and which generate a moment about their drive axis. Compared to the structural links, these conventional manipulator hinge designs provide the dominant contribution to the manipulator mass as well as its compliance.
A more recent focus on in-space missions has identified a need for long-reach, low-mass manipulators that can support operations for missions to Near Earth Objects, orbital debris removal, satellite and propellant depot servicing, rapid International Space Station resupply, and large telescope assembly. As with ground-based applications, the current state of the art for manipulators, the Shuttle and Space Station Remote Manipulator Systems (SRMS and SSRMS), represent conventional embodiments consisting of long lightweight tubular booms, connected by massive rotary torque hinge, gearbox and motor system. The SRMS and SSRMS have proven the benefit of long reach manipulators in the 15-18 meter class. The SRMS has a maximum reach of approximately 50 feet and can exert a maximum tip force of 12 pounds and has a design goal of 10 lbf/inch stiffness measured as deflection at the tip for the fully extended (straight) arm. The total weight (on Earth) of the SRMS is 905 lbf, with the hinges (shoulder, elbow and wrist) weighing 561 lbf and the links (upper and lower arm) having a combined weight of 108 lbf. The hinges dominate, at 84%, the combined mass of the hinges and links in the manipulator. In addition, the compliance of the hinges in rotation dominates the stiffness of the manipulator as measured at the tip. As the required reach for a manipulator increases, a conventional configuration suffers from the same rapid increase in mas as a ground-based manipulator.
While the SRMS and SSRMS have proven the benefit of long reach manipulators with the reach of both manipulators in the 15-18 meter class, manipulators with an even greater reach would provide many benefits. The SRMS's limited reach required an additional boom to augment its reach during inspection of the belly of the Shuttle Orbiter in support of return to flight following the Columbia disaster. Berthing operations benefit from longer reach because visiting space craft are intercepted at a greater separation allowing more time to accomplish the berthing maneuver. This additional separation allows capture at higher delta V's, reduction in the interface forces as well as additional time to execute contingency options. If the SSRMS had a longer reach, fewer power data grapple fixtures would be required along the space station truss and the SSRMS could reach a larger percentage of the space station. Future large space structures, such as large telescopes, space solar power and fuel depots would benefit from a longer reach manipulator during construction, repair and upgrade operations.
The manipulator architecture of the SRMS and SSRMS has limited scalability. Longer manipulators require large diameter booms and massive motor gearbox combinations to actuate the hinges, driving up weight and reducing packaging efficiency. In addition, the architecture does not lend itself to on-orbit repair, requiring the entire device to be returned to Earth for routine maintenance or repair. Further, the primary flexibility occurs at the hinges of these manipulators due to the collocation of the hinge drive gear system.
The structural efficiency of several column embodiments have been compared for space applications. Truss columns have been shown to be much more efficient than tubes as length and stiffness requirements increase, with tubular longeron trusses generally having higher efficiency than solid longeron trusses. Based on this, truss structures were used to develop long-reach manipulators such as the Space Crane. The Space Crane achieved a higher structural efficiency over the conventional boom/high-torque rotary hinge configuration by using trusses instead of cylindrical tubes for the links, and an offset linear-actuator/revolute hinge instead of a high-torque revolute hinge.
A manipulator is provided herein which provides improvements to existing structures and which overcomes the disadvantages presented by the prior art. Other features and advantages will become apparent upon a reading of the attached specification, in combination with a study of the drawings.